Reactor liquid cooldown method

ABSTRACT

A reactor liquid cool down method is provided. The method includes obtaining a warm recycle stream ( 102 ) from a reactor ( 101 ) and compressing the warm recycle stream ( 102 ), thereby producing a compressed warm recycle stream ( 104 ); mixing a compressed warm recycle stream ( 104 ) with a controlled liquid cryogen stream ( 110 ) in a stainless steel mixing zone ( 107 ), thereby producing a cool recycle stream ( 112 ), wherein the cool recycle stream has a mean fluid temperature, monitoring the mean fluid temperature and comparing the mean fluid temperature to a predetermined control valve set point, thereby defining a temperature deviation; modulating a temperature control valve ( 109 ) to vary the controlled liquid cryogen stream ( 110 ) in order to produce a temperature deviation that is less than a predetermined value, and returning the cool recycle stream ( 112 ) to the reactor ( 101 ).

RELATED APPLICATION

This patent application claims priority to U.S. Provisional PatentApplication Ser. No. 61/755,117 filed on Jan. 22, 2013, which is herebyincorporated by reference in its entirety.

BACKGROUND

In order to shorten downtime for turnarounds, refineries use coldnitrogen injected into reactor recycle loops to cool down reactorsquicker than with simply using the hydrocarbons in the system. Thissystem will reduce the amount of nitrogen required for most cooldowncycles by almost ⅔—increasing the value to the customer drastically.

Systems outfitted with piping of incompatible metallurgy are not able touse liquid nitrogen and the nitrogen must be vaporized and brought to aacceptable temperature before injecting into the customer's system(using mobile nitrogen vaporization units). Systems outfitted withstainless steel piping are able to inject liquid nitrogen directly,which requires far less nitrogen—usually around ⅓, but the majority ofcool downs are with cold gas. Both technologies are mature, althoughdirect injection generally requires a higher level of safetyconsciousness. Some customers with stainless piping are furtherreluctant to pursue liquid cooldowns because of the risk of recyclecompressor failure, or other failures that could result in liquidnitrogen reaching the reactor itself. The major drawback of cold gassystems is that the time it takes to perform the cool down to thecustomer's satisfaction, and the nitrogen usage—both of which offer anopportunity to create value for the customer through novel solutions.

SUMMARY

One embodiment of a reactor liquid cool down method includes obtaining awarm recycle stream (102) from a reactor (101) and compressing the warmrecycle stream (102), thereby producing a compressed warm recycle stream(104); mixing a compressed warm recycle stream (104) with a controlledliquid cryogen stream (110) in a stainless steel mixing zone (107),thereby producing a cool recycle stream (112), wherein the cool recyclestream has a mean fluid temperature, monitoring the mean fluidtemperature and comparing the mean fluid temperature to a predeterminedcontrol valve set point, thereby defining a temperature deviation;modulating a temperature control valve (109) to vary the controlledliquid cryogen stream (110) in order to produce a temperature deviationthat is less than a predetermined value, and returning the cool recyclestream (112) to the reactor (101).

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic representation of one embodiment of the presentinvention.

DESCRIPTION OF PREFERRED EMBODIMENTS

Illustrative embodiments of the invention are described below. While theinvention is susceptible to various modifications and alternative forms,specific embodiments thereof have been shown by way of example in thedrawings and are herein described in detail. It should be understood,however, that the description herein of specific embodiments is notintended to limit the invention to the particular forms disclosed, buton the contrary, the intention is to cover all modifications,equivalents, and alternatives falling within the spirit and scope of theinvention as defined by the appended claims.

It will of course be appreciated that in the development of any suchactual embodiment, numerous implementation-specific decisions must bemade to achieve the developer's specific goals, such as compliance withsystem-related and business-related constraints, which will vary fromone implementation to another. Moreover, it will be appreciated thatsuch a development effort might be complex and time-consuming, but wouldnevertheless be a routine undertaking for those of ordinary skill in theart having the benefit of this disclosure.

The proposed solution may include a stainless piping skid that may bemounted on a non-DOT trailer (capable of being pulled by non-DOT pickuptrucks). The customer's entire recycle stream is redirected throughtemporary piping into the skid, where liquid nitrogen could be injectedwithout risk to the customer's piping.

The skid would include automatic bypass and isolation valves as well asa temperature control valve and multiple thermocouples (for votingpurposes). The customer's stream would enter the skid through the firstisolation valve. After a sufficient length of pipe to ensure adequatemixing, the combined stream would pass over three thermocouples beforeexiting the skid through the second isolation valve back Into thecustomer's piping.

The thermocouples would be used to isolate and bypass the skid in theevent a predetermined low temperature limit was reached (to be agreedupon with the customer—2 out of 3 voting). The liquid nitrogen wouldenter the piping via a temperature control valve—the thermocouples wouldalso be used as the control point (also to be agreed upon with thecustomer). Liquid nitrogen pressure would be provided by a small mobilenitrogen pumping and vaporization unit or simply the centrifugal pump onthe liquid nitrogen transport. The skid would be controlled by a simplePLC. Power and air would be provided by the transport or pumper. In thismanner, customers with incompatible piping in their existing systemwould be able to enjoy the benefits of liquid cooldown.

Turning to FIG. 1, reactor 101 is to be cooled down. In one embodimentof the present invention, warm recycle stream 102 is removed fromreactor 101 and introduced into compressor 103. Compressed warm recyclestream 104 may pass through first isolation valve 106, after which itenters stainless steel mixing zone 107. Liquid cryogen stream 108 enterstemperature control valve 109, thus generating controlled liquidnitrogen stream 110, which then enters stainless steel mixing zone 107.Liquid cryogen stream 108 may be any compatible cryogen known in theart. Liquid cryogen stream 108 may be liquid nitrogen.

Compressed warm recycle stream 104 and controlled liquid nitrogen stream110 are mixed within stainless steel mixing zone 107, thereby producingcool recycle stream 112, which exhibits a mean fluid temperature. If thetemperature of warm recycle stream 102 deviates from a predeterminedtemperature, compressed warm recycle stream 104 may be bypassed throughline 115 and normally closed valve 105.

Temperature sensor 111 senses the mean fluid temperature, and transfersthis temperature information to temperature control valve 109. In oneembodiment of the present invention, three temperature sensors (111A,111B, 111C) are used, thereby allowing the voting of two out of three,in order to improve reliability and accuracy. The mean temperature iscompared to a predetermined temperature control valve set point.Temperature control valve 109 then adjusts controlled liquid nitrogenstream 110 in order to bring the mean temperature closer to thepredetermined temperature control valve set point.

Stainless steel mixing zone is of sufficient length to obtain the propermixing of controlled liquid nitrogen stream 110 and compressed warmrecycle stream 104. For example, if natural turbulence is the solemixing mechanism, as many as 100 diameters of mixing length may benecessary. If one or more static mixer is used, then less than 10diameters will be necessary, preferably between 4 and 6 diameters, morepreferably 5 diameters. Once the mixing is complete, cool recycle stream112 passes through second isolation valve 113 and is returned to reactor101.

A reactor liquid cool down method, comprising;

-   -   obtaining a warm recycle stream (102) from a reactor (101) and        compressing the warm recycle stream (102), thereby producing a        compressed warm recycle stream (104),    -   mixing the compressed warm recycle stream (104) with a        controlled liquid cryogen stream (110) in a mixing zone (107),        thereby producing a cool recycle stream (112), wherein the cool        recycle stream has a mean fluid temperature,    -   monitoring the mean fluid temperature and comparing the mean        fluid temperature to a predetermined control valve set point,        thereby defining a temperature deviation,    -   modulating a temperature control valve (109) to vary the        controlled liquid cryogen stream (110) in order to produce a        temperature deviation that is less than a predetermined value,        and    -   returning the cool recycle stream (112) to the reactor (101).

The reactor liquid cool down method as described above, furthercomprising;

-   -   monitoring a first mean fluid temperature of the warm recycle        stream (102),    -   closing the temperature control valve (109), closing a first        valve (106), a closing second valve (113), and opening a bypass        valve (105) if the first mean fluid temperature is less than a        predetermined minimum temperature,        wherein the first valve (106) and the second valve (113) isolate        the stainless steel mixing zone, and        wherein the bypass valve (105) allows the warm recycle stream        (102) to return to the reactor (101).

The reactor liquid cool down method as described above, wherein themixing zone (107) is stainless steel.

The reactor liquid cool down method as described above, wherein the meanfluid temperature is monitored by temperature indicators.

The reactor liquid cool down method as described above, furthercomprising at least three temperature indicators, wherein a two out ofthree voting protocol is utilized.

The reactor liquid cool down method of as described above, wherein theliquid cryogen is liquid nitrogen.

What is claimed is:
 1. A reactor liquid cool down method, comprising;obtaining a warm recycle stream from a reactor and compressing the warmrecycle stream, thereby producing a compressed warm recycle stream,mixing the compressed warm recycle stream with a controlled liquidcryogen stream in a mixing zone, thereby producing a cool recycle stream, wherein the cool recycle stream has a mean fluid temperature,monitoring the mean fluid temperature and comparing the mean fluidtemperature to a predetermined control valve set point, thereby defininga temperature deviation, modulating a temperature control valve to varythe controlled liquid cryogen stream in order to produce a temperaturedeviation that is less than a predetermined value, and returning thecool recycle stream to the reactor.
 2. The reactor liquid cool downmethod of claim 1, further comprising; monitoring a first mean fluidtemperature of the warm recycle stream, closing the temperature controlvalve, closing a first valve, a closing second valve, and opening abypass valve if the first mean fluid temperature is less than apredetermined minimum temperature, wherein the first valve and thesecond valve isolate the stainless steel mixing zone, and wherein thebypass valve allows the warm recycle stream to return to the reactor. 3.The reactor liquid cool down method of claim 1, wherein the mixing zoneis stainless steel.
 4. The reactor liquid cool down method of claim 1,wherein the mean fluid temperature is monitored by temperatureindicators.
 5. The reactor liquid cool down method of claim 4, furthercomprising at least three temperature indicators, wherein a two out ofthree voting protocol is utilized.
 6. The reactor liquid cool downmethod of claim 1, wherein the liquid cryogen is liquid nitrogen.